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March 6, 2015

AN OLD-TIMEY QUESTIONS AND ANSWERS SESSION.

Q: I was on a flight and the emergency hatch next to us made the most awful squealing noise during takeoff and landing. We were told it was nothing to worry about, but needless to say I spent the whole flight a nervous wreck.

What you describe isn’t terribly uncommon. Such sounds are caused by small leaks around the door seal as the plane’s pressurization levels fluctuate (sort of like those that result when you stretch the neck of a balloon as it deflates). It’s noisy but it couldn’t be less dangerous. Tiny air leaks pose no hazard. There’s always a little bit of flexibility built into certain airframe components — there has to be — and this is one result. Usually, after a while, the door will settle into a sweet spot and the sound will stop. A similar thing happens in the cockpit sometimes around the seals of the sliding side windows.

On some aircraft — usually smaller ones — the door seal consists of an inflatable gasket. Occasionally this gasket will burst or deflate, causing a gradual depressurization, which is a big hassle that could result in a diversion (having to fly at a lower altitude means having to burn more fuel). The 19-seaters I used to fly had an inflatable seal around the main boarding door. When it failed, as it did once in a while, it made a hideous noise — a sort of hypersonic flatulence, like a motorcycle roaring through the cabin. It scared the hell out of the people closest to the door, but all in all it was harmless.

Q: We flew from Miami to JFK on an MD-80. The jet is laid out with two seats on one side of the aisle and three on the other. The question came up: does the asymmetric 3/2 configuration cause any kind of imbalance?

No. Even on a smallish plane like the MD-80 series (a derivative of the even older DC-9), the imbalance is less than negligible. In the cabin, longitudinal balance is a lot more important that lateral balance. But even there it tends to be a minor factor — at least on bigger planes, where the weight of passengers makes up a surprisingly small percentage of a plane’s overall weight. As covered in the first chapter of my book, in the case of a fully loaded 747, the weight of 400 passengers plus their luggage accounts for less than 10 percent of the plane’s total weight.

Q: What are the normal climb rate and decent rates for jetliners? I know it probably varies, but as a student pilot I was wondering how steep the average rates are.

Indeed it varies. It varies so much that I’m not sure what answer to give you. Really there’s no such thing as a “normal” climb or descent rate. It depends on the weight of the plane, your altitude, the temperature, how many feet you’re trying to lose or gain, ATC constraints, etc. During cruise, if we have to climb or descend only slightly — say 1,000 or 2,000 feet — I’ll usually set up the autopilot for a mild, 500 foot-per-minute rate. On the other hand, I’ve seen rates as high as 5,000-6,000 feet-per-minute both climbing and descending. In the 757s and 767s that I fly, planes I fly, takeoff and initial climb can be anywhere from 2,000 to 5,000 feet-per-minute, depending on the aircraft weight and what segment of the departure profile you’re flying.

Five thousand feet-per-minute sounds like a lot, but so long as any climb or descent is initiated gradually, with minimal change of g-force, even the steepest rates will be barely detectable from a passenger’s seat-of-the-pants perspective.

Q: How come it feels as if Ryanair pilots land at higher speeds than pilots at other carriers? And Ryanair’s pilots always seem to land hard.

Landing speed isn’t subjective. Approach and landing speeds are determined by weight, wind, and flap setting, and aren’t really negotiable. No airline’s pilots land faster (or slower) than anybody else’s. As to the second part of your question, Ryanair tends to serve smaller, outlying airports that often have shorter, less forgiving runways. The technique when landing on a short runway is to not try and finesse it. A slightly firmer touchdown using less runway is preferable to a smoother touchdown that wastes pavement.

Q: Is it true that airlines always hold out one seat in first class for the pilot? And does that mean if, online, it shows two seats left in first, really there is only one?

Long-haul flights carry extra pilots that work in shifts or in teams. The pilots on their rest break retire to a designated rest area. On some aircraft this means a first or business class seat that is pre-reserved for crew. These seats are considered “booked” just as if a passenger had reserved them. So, if an airline says two seats are open, then yes, two seats are open.

On most bigger planes, though, the crew rest quarters are entirely separate from passenger seating. Typically there are bunks or other accommodations tucked away somewhere — above, below, or on the main passenger deck — and accessible only to the pilots (flight attendants have their own rest quarters located elsewhere). In that case, no, there are no seats held for the pilots.

All of this is separate from crews that might be “deadheading.” That is, pilots or cabin staff who are riding as passengers as part of a repositioning assignment. In this case too, the seats occupied by these employees are blocked ahead of time and will not show up as open inventory.

Q: After landing and taxiing into the apron, we came to a stop a couple of hundred feet from the terminal, shut down the engines, and finally were towed to the gate by a tug-tractor. This seems to be common procedure at many airports. What’s the reason?

Many gates at congested airports are tow-in only. The proximity of ground equipment, vehicles and workers makes it hazardous to maneuver using the engines. Even at low power a jet engine produces a considerable amount of thrust that could easily flip over a baggage container — or a person.

Q: I understand for example that a Boeing 747-400 is the -400 variant of the basic 747 model. But what does it mean when I see a picture of an aircraft and the photographer displays the code 747-430? >

Maximum geek on this one. The second two numbers of the suffix — the “30” in this case — are the customer code. Boeing assigns each airline has its own two-number code. The 30 code (I Googled it) belongs to Lufthansa. All 747-400s sold to Lufthansa are 747-430s. A 777-200 delivered to United Airlines would be a 777-222. And so on. This is to help account for engine type, cabin configuration and other customer-specific options. Even if these planes are subsequently sold to another carrier, the designation remains.

The original 747s, the -100s, were actually 747-121s. The 21 suffix belonged to Pan Am.

One area that I get confusion on is the belief that a direct flight is the same as a non-stop flight. When a Non-Stop is self explainatory. A Direct flight will have landing and takeoffs in route to the end of the flight. I recall a flight from DC that was direct I was going to clarksburg WV and had a stop in clarksburg, Parkersburg, and finally got to morgantown (back when they still had scheduled service). (I felt like I was on a bus) but it was a direct flight because I didn’t have to connect to another aircraft.

I know it sounds silly, but I worry about the hatch door closing on a jet liner and there being limited air in the cabin. I’ve heard that there is enough air circulating to cool a 3 bedroom apartment. Is that true?

As usual, after the FlyDubai crash in Rostov-on-Don, most of the media did an awful job covering the story. Initial reports claimed 20 meter per second winds, which equates to about 38 knots. In those conditions, should the plane have been rerouted to a nearby airport or do 38 knot winds pose little danger to a landing aircraft?

Why not fit cameras at strategic positions along or imbedded in the fuselage that would allow cockpit crew to see tail section and/or underwing /engine areas? I recall stories about pilots being unaware of structural failures in tail sections, underwing components and fighting to maintain control, unaware that major control components were damaged or missing.
Are there planes with cabin cameras fitted that enable cockpit crew to see what’s happening in the cabin?

As to the leaking door topic above, there’s an amusing post over on the VC10 web site about a leaky door seal that was fixed by stuffing boxes and boxes of tampons around the door. It did the trick, and when they arrived and popped the door dozens of frozen tampons spilled out onto the tarmac – right in front of a diplomatic event being held for a VIP.

Question: The maximum temperature limitation for takeoff is ISA +34degrees C. Which is the highest temperature that will allow a takeoff from a 7,000-foot pressure altitude airport? using a CX-2 pathfinder flight computer. Is the answer in the instruction booklet wrong?

Apart from all that automation fantasizing (sparked by Germanwings once again) which of course hideously neglects loads of the true facts of real flying – when Capt. Sullenberger watered on the Hudson, as he was touching down the airplane did a slight nose-up by itself that even he hadn’t been aware of (he said that in an interview that I happened to see the videotaping of, stating the watering could have been still a bit smoother if the airplane had let him. Never mind implications about tears in the hull and the thing sinking less slowly, albeit leading only to a few cases of mostly non-life-threatening hypothermia in this case gone well). Needless to say I can’t find any reason not to believe this detail of Capt. Sullenberger’s account (and the manufacturer of the airplane confirmed that they did this). So much for complete control of the PF.

That said, I know it would be a lot more complex of course, but how can it be that a fly-by-wire system micromanage the pilot’s control input on its own authority in a critical situation – statement in mind that the pilot is always in full control (what rule was Sullenberger flying his Airbus glider anyway?) – but keep nice and quiet when the autopilot is set to something about one mile below ground level (my calculation from what was reported w.r.t. the Germanwings disaster)? Seeing as the autopilot on an Airbus (not sure if that was the same model) would even refuse to work at all when some higher-level systems can’t make sense of some readings from the environment (I forget what it was exactly, something about AOA envelope in a non-crash incident investigated by the BfU), this doesn’t really add up. Well I guess I mixed a few cases with not really identical features, but would you mind commenting on how things on that level (and others) make sense from the larger perspective of augmented (or something) flying?

And many thanks for a great site and QA. Sorry for involuntarily choosing this thread for posting my question – my browser gave me something like a quiet comments closed in the place I meant to put it. Please do move it as you see fit.

I have to take a plane that arrives 6 hours before my departure, that means the plane would be spending 6 hour in the ground before it flies. I seen more common that a plane arrive and only stay in the ground for 1:30 hour and then flies.

So I’m worry that the 6 hours in the ground could not be safe left alone or with less supervision

Is it more safe to fly an airline that dose;t stay on the ground too long like 6 hours ?

I am planning my first overseas trip from Australia to Los Angles and it is a 13 hour flight across the Pacific. I am wanting to know if a 777 is safe to fly over the pacific (as it only has two engines and not 4) or a 15 year old 747 with 4 engines but it is older then the 777. If something happened like engine problems or a fire and it takes place within the middle of the 13 hour flight past places like Midway Island where you could land are there any other places to land in the middle of the pacific at night or day? Or does it all come down to luck?

It isn’t about luck. The fact that oceanic crossings are as remarkably safe as they are is the result of lots of hard work, technological advances and training. In any case, you’re over-thinking it. In practical terms there is virtually no correlation between aircraft type, number of engines and transoceanic safety. Two-engine planes have been crossing the oceans for over thirty years now without so much as a single engine-related fatality. Thousands of two-engine planes make such trips every day.

Thank you for that. I am sure it is fine and the 777 is a safe plane. As you said it is designed for this type of flight. I watched the making of it and i am comforted to know a lot of research went into the design of it.

The reason for customer codes is partly due to engines since customers pick different engine manufacturers, and sometimes configuration. And mostly because customers get to customize their planes. One documentary I watched claimed the 747-400 had many options, including whether the clipboard clip for the pilots goes on the side or on the top. Boeing were supposedly trying to limit the amount of customisation, as it has effects on assembly time, parts inventory and logistics. This can also cause problems when the planes are sold to other airlines second hand since they aren’t all identical.